If those emails “are not showing online” in your iCloud trash / bin folder but are still showing in eM Client and you carn’t delete them, then try running the manual database repair which should then clear the trash emails that won’t delete.
To manually repair eM Client database for Windows, see @Gary post link below.
https://forum.emclient.com/t/item-cannot-be-delete-from-trash/95660/2
To manually repair eM Client database for Mac, do the following.
First “close eM Client” and then “open the Terminal app via either Launchpad or Utilities”.
Then Paste and run the following command.
/Applications/eM\ Client.app/Contents/MacOS/eM\ Client /dbrepair
Then reopen eM Client and see if they are gone.